Fimo is a polymer clay that you bake in the oven at a mere 275 degrees. Because
of its peculiar properties, it retains sharp delineation between colors, but at the
same time bonds well with itself. As a result, you can squish it, roll it, whatev,
and it still retains sharp lines. Well, it's hard to explain, easier to show you.

Here's a sample, once you see it you'll realize you know exactly what it
is...

One of the interesting things about fimo is that it's sorta like nuclear
isotope: it's
only good if it's fresh. When fimo gets hard and crumbly, as it ages, you
have to mix it with fresh or just throw it out. That's why you will see fimo
afficionados fondling the fimo at the art store: you have to squeeze it to
see
if it's fresh. There is, of course, a bit of leeway. If your fimo is a bit
old you simply moosh it around between your warm palms until it gets soft and
squishy. If it continues to shred in little bits, it is time to throw it in
the dustbin.